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Porous isotactic polypropylene from supercritical propane solution: Synthesis and characterization
Abstract
Solid-supercritical fluid (S-SCF) and liquid-vapor equilibria (cloud-point pressures) for iPP/propane systems were determined. Liquid-vapor equilibria below S-SCF equilibria temperatures for iPP/propane were obtained by studying the atactic polypropylene (aPP)/propane system. Modeling of these systems by the Sanchez-Lacombe lattice fluid theory required empirical adjustment of mixing parameters. Cloud-point pressures for polyolefins of increasing branch length and some poly(ethylene-co-octene) copolymers in propane were also determined. They decrease with increasing percentage of carbon in the branches. Crystallization of iPP from single phase systems was achieved by controlling temperature and pressure. Under most conditions, crystallizations of unnucleated iPP resulted in large (100+ $\mu$m) microspheres having poor mechanical coherency. A highly effective nucleating agent, dibenzylidene-d-sorbitol (DBS), was added to promote nucleation and coherence, but requires a cosolvent for solubilization. S-SCF equilibria for DBS in propane/1-propanol mixtures were determined as well as changes in the phase behavior of aPP/propane with the addition of an alcohol and is summarized in terms of changes in critical behavior. Surface areas and pore size distributions (PSD) in the mesopore range (20 to $\sim$500 A) were determined by analysis of nitrogen adsorption-desorption isotherms. Surface areas ranged from 120-180 m$\sp2$/g with most probable pore sizes, based on a cylindrical pore model, of between 100-200 A. This pore size is supported by small angle x-ray scattering data analyzed by a model which treats the pores as a distribution of spherical aggregates. A more specific model is proposed in which the microsphere contains a dense core defined by a radius beyond which fibrillation and gas adsorption sets in. The high surface area of porous iPP is attributed to as yet unknown details of the organization of iPP lamellae on the nanoscale.
Subject Area
Polymers|Materials science|Chemical engineering
Recommended Citation
Whaley, Paul D, "Porous isotactic polypropylene from supercritical propane solution: Synthesis and characterization" (1996). Doctoral Dissertations Available from Proquest. AAI9639050.
https://scholarworks.umass.edu/dissertations/AAI9639050